In a packaging material for light-sensitive material, for a barrier material having a dehumidifying function and light-shielding property, various technologies have been developed for keeping physical strength, dehumidifying and light-shielding properties.
For keeping strength, materials described in Japanese Patent Publication Open to Public Inspection (hereinafter, referred to as "Japanese Patent O.P.I. Publication") Nos. 237640/1986, 181944/1987 and 283944/1988 and Japanese Utility Publication Open to Public Inspection No. 25538/1987 are cited. As a packaging material using a straight-chained low-density polyethylene (LLDPE) having excellent film physical property, materials described in Japanese Patent O.P.I. Publication Nos. 18547/1987, 289548/1988, 290741/1988, 270535/1989, 946341/1989, 64537/1990, 146539/1990 and 196238/1990 are known. In addition, with regard to the light-shielding property, light-shielding materials preferably used for a light-shielding layer are described in Japanese Patent O.P.I. Publication Nos. 85539/1988, 82935/1989, 209134/1989, 94341/1989, 165140/1990 and 221956/1990. With regard to the dehumidifying property, packaging materials using aluminum foil or depositing metal layers are described in Japanese Patent O.P.I. Publication Nos. 77532/1989, 251031/1989, 186338/1990 and 17825/1990. In addition, materials considering an dust shielding property is known in Japanese Utility Publication No. 35540/1991.
The above-mentioned packaging materials include a tube type and sheet types composed of several multi-layered structure.
The tube type packaging material can be easily manufactured by means of the inflation method. Namely, molten polyethylene containing carbon black is extruded from a disc die mounted on an extruder. Inside the extruded tube type film, air is blown so that the film is gradually swollen up to a prescribed diameter. When the extruded film is chilled and solidified, it is folded by means of a guide roll or a nip roll, and is then wound. Thus, a continuous tube is obtained. The resulting continuous tube is cut to appropriate lengths, and concurrently with this, one side of the cut end is sealed by means of heat-sealing or folded by means of heat press or adhesive tape. Thus, an envelope is obtained. Into this envelope, a light-sensitive material is inserted through the open end manually, and then, the open end is sealed with a heat press or adhesive tape to obtain a packaging material.
It is necessary for the above-mentioned tube type packaging material to be prepared for each envelope width. Since the kind and the size of light-sensitive material products are very varied and suitable clearance of envelopes housing such products are fixed, accordingly, the number of envelope sizes becomes large, for which tubes of many width sizes must be prepared. Accordingly, there occurs a problem that productivity is lowered and inventory control becomes complex. More serious, however, is that, firstly, automatic packaging is difficult and, secondly, it is difficult to provide added value such as strength-enhancing and dehumidifying property so that protection for the light-sensitive material is insufficient.
Accordingly, sheet type packaging materials composed of several multi-layered structure are commonly used. As the above-mentioned sheet type packaging materials, those having a laminated layer structure and each layer having a specific function, as shown in FIGS. 1 through 5 are preferably employed. The above-mentioned sheet type packaging materials have an outer heat-durable layer so that the sheet can be subjected to heat sealing by means of a heat press for facilitating to make a tube shape. If the packaging material is too wide width, it can be cut as appropriate before or after preparing the tube. Therefore, it can be used for packaging materials having different sizes as desired. Therefore, it is preferable in terms of inventory control and productivity.
Paper (unbleached, semi-bleached and fully-bleached kraft paper) is cited as a typical material used for the heat-durable layer. Those whose weight is 45-190 g/m.sup.2, and those whose weight is 50-90 g/m.sup.2 are preferred from viewpoint of envelope-finishing property and strength. In addition to paper, resin films, such as polyethylene terephthalate, nylon and polypropylene, which has higher heat-strength compared to a heat-sealed can be used for the heat-durable layer.
Among layer laminations wherein functional layers are adjacent to each other, layer lamination, having a lamination layer, as shown in FIGS. 1 through 4 are layer laminations wherein the lamination layer(s) adhered between each functional layer. The lamination layer can be formed by means of an extrusion lamination method, a dry lamination method, a wet lamination method and a hot melt lamination method. When layer lamination is made of resin films, the extrusion lamination method or the dry lamination method are commonly used. In FIG. 5 is a layer lamination is directly molten by superposed molten extrusion.
Functions of light-shielding, strength-enhancing and heat-melting which are essential for the packaging material for light-sensitive material may be shared by each layer. However, if either of the light-shielding function or the strength-enhancing function is destroyed, it leads to the destruction of all functions of the packaging material. Therefore, in terms of strength of the packaging material, it is preferable that one layer has both functions. Therefore, the light-shielding, strength-enhanced and heat-sealed in FIGS. 1 through 4 exhibits a layer having functions of light-shielding, strength-enhancing and heat melting functions. The intermediate light-shielding and strength-enhanced layer in FIG. 5 exhibits a layer having functions of light-shielding and strength enhancing. For the above-mentioned layer wherein functions of light-shielding and strength enhancing are concentrated, a sheet formed by being cut with a cutter before a black polyethylene tube containing carbon black is wound can be employed as a major constituting material capable of being produced most simply.
In FIG. 1, the layer lamination of the heat-durable layer and the lamination layer is separated from a single light-shielding, strength-enhanced and heat-sealed. This is a constitution in which two laminated sheets and a single layer sheet are symmetrically superposed on the upside and downside of the light-sensitive material packaged and heat melting occurs between the laminated sheets and the single sheet due to the lamination layer when finishing the envelope due to heat press. Since two sheets of the envelope wall of the resulting packaging product can extend independently, they easily absorb shock so that the packaging product is resistant to impact or tearing. On the contrary, however, there is the shortcoming that production loss easily occurs when finishing the envelope.
The above-mentioned sheet type packaging materials composed of several layers lamination have satisfied requests in terms of strength, function and control to some extent. However, there are major shortcomings in terms of recycling or incinerating the materials. Namely, the film raw materials of each layer constituting the laminated sheet, such as the heat-durable layer, the lamination layer, the dehumidifying layer, the light-shielding and strength-enhancing, the heat-sealed and the light-shielding, strength-enhancing and heat-sealed, are all different from each other. Consequently, the separation is so difficult that recycling is difficult. In addition, when metals such as aluminum are used for the dehumidifying layer, metal dust remains when the packaging product is incinerated.
The present inventors proposed a packaging material for light-sensitive material composed of at least three laminated layers, mainly made of polyethylene, containing at least one light-shielding layer, in which recycling can be conducted without need of separating each layer, which were disclosed in Japanese Patent O.P.I. Publication No. 75339/1994 and Japanese Patent Application No. 16020/1995. The packaging material for light-sensitive material have satisfied requests in terms of strength-enhancing, functions and control to some extent. However, it turned out that there are still problems in terms of physical strength during transportation requested from viewpoint of further severe transportation circumstances.